usb: host: xhci: Demote obvious misuse of kerneldoc to standard comment block

usb: host: xhci: Demote obvious misuse of kerneldoc to standard comment block

No attempt has been made to document the demoted function here.

Fixes the following W=1 kernel build warning(s):

 drivers/usb/host/xhci.c:1285: warning: Function parameter or member 'desc' not described in 'xhci_get_endpoint_index'

Cc: Mathias Nyman <mathias.nyman@intel.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20200703174148.2749969-14-lee.jones@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>